This invention relates to an apparatus for controlling an exhaust gas recirculation valve (hereinafter referred to as an EGR valve) which is disposed in an exhaust gas recirculation system.
FIG. 1 is a conventional schematic explanation diagram of an engine exhaust system.
In this apparatus for controlling the EGR valve, the opening and closing of the control valve 11 is controlled by, for example, a stepping motor M of a hybrid PM type 4-phase construction or the like. An open-loop control of the stepping motor M by a stepping angle contributes to a control over the degree of the opening of the control valve 11.
Such a control apparatus using this kind of stepping motor M imposes a restriction on the control over the degree of the control of the control valve 11 because the degree of the opening of the control valve 11 can be controlled only by the stepping angle of the stepping motor M, the control valve 11 has a limited resolution of the controllable opening. In addition, the stepping motor M has a limited open-loop control response characteristic due to the possible occurrence of a stepping-out phenomenon. Once the stepping-out phenomenon has occurred, the reliability falls as an error is still contained uncompensated in the control amount.
To this end, the conventional apparatus for controlling an EGR valve gives a predetermined return torque to the control valve 11 in the opening or closing direction by urging means and, by the application of a unidirectional current to a direct current (DC) motor (hereinafter referred to also as a DC motor) gives a motor torque to vary the control valve 11 in the closing direction, and opens and closes the control valve 11 by the balance of these torque. An arrangement is described in Japanese Published Unexamined Patent Application No. 122059/1998. This arrangement includes an open loop control system for controlling an open loop of the DC motor such that a motor torque is generated in corresponding with a target opening and closing positions of the above control valve 11; and a feedback control system for feedback-controlling the DC motor based on a deviation between input data corresponding to the target opening and closing positions of the control valve 11 and detected data of the current opening and closing positions of the control valve 11.
FIG. 2 is a characteristic diagram showing the relationship between a motor torque and an opening and closing position of a control valve in an EGR valve of torque balance drive system.
First, the driving system using this DC motor will be described. In case the degree of the opening of the control valve 11 is feedback-controlled in a DC servo motor system, the generated torque of the DC motor is continuously controlled by feeding back the degree of the opening of the control valve 11 through unintermitted detection with a position sensor such as a sliding resistor type. Theoretically, the continuos control over the generated torque of the motor M promotes infinite reduction of the resolution. Further, the DC motor does not cause the control error due to the stepping-out as with the stepping motor M and, therefore, the response can be improved accordingly as compared with the case where the stepping motor M is used, thereby improving reliability.
This kind of apparatus for controlling the EGR valve using the DC motor adopted a so-called torque balance system. The apparatus gives a predetermined return torque in the closing direction (or in the opening direction) by means of a spring as urging means, gives a variable motor torque in the opening direction (or in the closing direction) by unidirectional power feeding to the DC motor and controls the valve opening and closing by the balance of these torque.
In case this kind of driving system is adopted, since the EGR valve is constantly given the return torque, there occurs a hysteresis, due to friction, as shown in FIG. 2 between the operating characteristic A when the control valve 11 is opened by increasing the motor torque and the operating characteristic B when the control valve 11 is closed by decreasing the motor torque. The inclination of the operating characteristics A, B varies depending on the spring constant of the spring which gives the return torque, and the operating characteristics A, B shift to the right or to the left in FIG. 2 depending on the magnitude of the set torque.
Now, in order to control the control valve 11 having this kind of operating characteristics, suppose that a method is admitted, in which the DC motor is under the control of a PI (proportional) I (integral) control based on a deviation between the input data corresponding to the target opening and closing position of the control valve 11 and the detected data of the current opening and closing position of the control valve. In this case, owing to the relation of the operating characteristics as shown in FIG. 2, it becomes difficult to stabilize the control valve 11 in the target opening position.
In other words, in order to open the control valve 11 to the target opening position by increasing the motor torque, the P gain and the I gain must be increased to take the control along the operating characteristic A in FIG. 2. However, when the motor torque is increased under the control of this kind, the deviation of the opening position of the control valve 11 becomes xe2x80x9c0xe2x80x9d as soon as the control valve 11 is opened to the target opening position. The P component thus becomes xe2x80x9c0xe2x80x9d and the I component is cleared, with the result that the control valve 11 begins to close by the return torque.
FIG. 3 is a characteristic diagram showing the relationship between the time and the opening and closing position in the EGR valve.
At an initial stage, the control valve 11 begins to close (at the time the deviation is small), since the P and I components are both small, the motor torque cannot overwhelm the return torque, with the result that the deviation becomes large. Thereafter, even if the deviation becomes large to a certain degree, the motor torque and the return torque balance with each other, and therefore the closing operation of the control valve 11 cannot stop abruptly due to the inertia of the DC motor M. The control valve 11 thus cannot be operated in the opening direction immediately. If the gain is made large such that generate a relatively large motor torque is generated even when the deviation is small, there will be a vicious cycle that incurs an increase of the overshooting and undershooting as shown in FIG. 3.
FIG. 4 is longitudinal sectional view of the RGR valve.
An apparatus for controlling the control valve 11 in a so-called torque balance drive system using the DC motor M will be made in consideration of the above situation with reference to FIGS. 4 to 7.
Referring to FIG. 4, reference numeral 1 denotes a valve body having formed therein a passage which forms a part of an exhaust gas recirculation passage c interposed in a recirculation system of the exhaust gas. By moving upwardly the control valve 11 as illustrated to contact a valve seat 12, the exhaust gas recirculation passage c is closed and, by moving downwardly the control valve 11 to apart from the valve seat 12, the exhaust gas recirculation passage c is opened.
Reference numeral 2 denotes a motor case for housing therein a DC motor 20. In the DC motor 20, reference numeral 21 denotes a rotor around which a coil 22 is wound, and reference numeral 23 denotes a yoke provided with a magnet 24. The upper end of the rotor 21 is rotatably supported on the motor case 2 by a sliding-ball 25 and a rotor shaft 26, and the lower end of the rotor 21 is rotatably supported on the valve body 1 by a bearing 27. A commutator 28 is attached to the upper end of the rotor 21, and a motor brush 30 provided on the motor case 2 is urged by a brush spring 29 into contact with the commutator 28.
Reference numeral 40 denotes a position sensor for detecting the rotational position of the rotor 21, and the position sensor is so arranged that its resistance value changes deepening on the rotational position of the rotor 21. This position sensor 40 and the motor brush 30 are connected by a connector terminal 3 to the control apparatus which will be described hereinafter.
Inside the rotor 21, a motor shaft 31 is screwed. The rotation of the motor shaft 31 is prohibited by a guide bush 13 provided on the body 1. It therefore follows that the motor shaft 31 moves upward and downward depending on the amount of rotation of the rotor 21. A valve shaft 14 is provided in contact with the lower end of the motor shaft 31, and an intermediate portion of the valve shaft 14 is guided by a guide seal 15 and a guide plate 16 so as to be movable upward and downward. The control valve 11 is attached to the lower end of the valve shaft 14.
Reference numeral 17 denotes a guide seal cover. Between a spring sheet 18 mounted on the upper end of the valve shaft 14 and the guide plate 16, a spring 19 is interposed for urging the valve shaft 14 in an upward direction, i.e., in the closing direction of the control valve 11.
The control valve 11 thus constituted in this manner is driven by a torque balance system as described above. In other words, the EGR valve gives a predetermined return torque in the closing direction of the control valve 11 by the spring 19 as the urging means, and also gives a variable motor torque in the opening direction of the control valve 11 by the unidirectional power feeding to the DC motor 20. By the balance of these torque, the control valve 11 is opened and closed.
FIG. 5 is a schematic diagram showing an engine control apparatus (referred to as ECU) 100 in the so-called torque balance device system using a DC motor. The motor driving voltage is determined by a control part 50 employing a microcomputer.
Referring to FIG. 5, reference numeral 52 denotes a battery. Reference numeral 53 denotes a motor driving voltage converting part for converting the output of the control part 50 and for supplying the converted output to the DC motor 20. The motor driving voltage converting part comprises a Zener diode 53a; a diode 53b for supplying the unidirectional current flow to the DC motor 20; a field-effect transistor (FET) 53c; and an interface 53d provided between the control part 50 and the FET 53c. Reference numeral 56 denotes a regulator to generate a driving voltage (5V) of the control part 50.
The control part 50 receives, through interfaces 58, 59, respectively, a detected signal from an operating state amount sensor 57 mounted on each part of the vehicle such as a crank angle sensor or the like, as well as that from the position sensor 40. The position sensor 40 in this example is provided with a movable contact part 42 for moving on a resistor 41 to which a constant voltage (5V) is applied from a voltage supply part 60. By the movement of the movable contact part 42 accompanying with the rotation of the rotor 21, a voltage corresponding to the rotating position of the rotor shaft 31 is outputted, as a detected signal, from the movable contact part 42.
Further, the above motor driving voltage converting part 53 switches on and off the voltage to be applied to the DC motor 20 at a constant period. The FET 53c is switched on and off by a pulse-width modulation (PWM) signal depending on the ratio of the on-time and the off-time per a period (driving duty), so that an average driving voltage to be applied to the DC motor 20 is controlled.
Since the above control part 50 controls the entire engine, the control of the DC motor 20 will be made during the intervals of the engine control, with the result that the optimum control is difficult. As a solution, an exclusive control circuit for the EGR valve is necessitated. This exclusive control circuit must be integrally assembled into the EGR valve. It follows that, if the control circuit is configured by a digital circuit using a microcomputer, the control circuit cannot be assembled into the EGR valve which reaches a temperature of 100 Ec or more because the microcomputer has a low heat-resistant temperature. In addition, the digital circuit has a complicated and costly circuit configuration.
This invention has been made to solve the above and other problems and has an object thereof is to provide such an exclusive control circuit for the EGR valve consisting of an analog circuit, which is able to resist to a high temperature, and has a simple and inexpensive circuit configuration.
An apparatus for controlling an exhaust gas recirculation (EGR) valve according to the invention comprises a computing circuit for outputting a control signal based on a target value signal indicative of the degree of a valve opening given from the outside and a current position signal of the valve; a voltage-duty converting circuit for changing the duty of the output signal based on the control signal; and a motor driving circuit for driving a DC motor by the output signal of the voltage-duty converting circuit.
Therefore, since such a circuit part of a lower heat-resistant temperature as a microcomputer is not used, the control apparatus can be integrally assembled directly into the EGR valve. In addition, since the control apparatus is constituted by analog circuits, the apparatus has a simple and inexpensive circuit configuration.
In the apparatus for controlling an EGR valve according to this invention a driving force in a normally-valve-open direction is given to a motor shaft of the motor with a force smaller than an urging force of a return spring so as to hold the motor shaft and a valve shaft in contact with each other.
Therefore, by the urging force of the return spring, the control valve can surely be held in the valve-closed state and also, when the control valve is opened, the control valve can be opened as soon as the DC motor is started.
In the apparatus for controlling an EGR valve according to this invention the maximum output voltage of the computing circuit and a 100% duty input voltage of the voltage-duty converting circuit coincide with each other.
Therefore, it is possible to improve the response characteristic.
In the apparatus for controlling an EGR valve according to this invention the computing circuit is provided with a negative hysteresis generating circuit.
Therefore, it is possible to reduce the hysteresis attributable to the urging force of the return spring by the output of the control circuit, with the result that the control valve is controllable with a higher accuracy and a good response characteristic.
In the apparatus for controlling an EGR valve according to this invention the negative hysteresis generating circuit is configured by at least one or more Zener diodes.
Therefore, it is possible to provide the negative hysteresis generating circuit having a simple configuration.
In the apparatus for controlling an EGR valve according to this invention the negative hysteresis generating circuit is configured by one or more diodes, or a combination of the one or more diodes and a resistor.
Therefore, it is possible to provide the negative hysteresis generating circuit of a simple configuration.